1. Field of the Invention
This invention relates generally to photoresist compositions and more specifically to photoresist compositions for use in the manufacture of printed circuit boards and packages of printed circuit boards.
2. Prior Art
Printed circuit boards and their manufacture using photoresists as negative masks during conductive metal plating processes are not new.
Printed circuit board designs using a "permanent" resist are also known. A permanent resist is a negative plating mask which is not removed from the printed circuit board substrate after plating, but rather becomes a part of the printed circuit board structure. Permanent resist printed circuit boards are described, for example, in U.S. Pat. No. 3,982,045 issued Sept. 21, 1976 to Kukanskis.
Attempts to manufacture useful permanent resists and printed circuit boards and packages using such a resist have uncovered a number of difficulties. One such difficulty is that there has not heretofore been available a UV-sensitive photoresist material which can be coated onto a substrate at cross-sectional heights of at least about 0.0015 inch and which will resist delamination in response to temperature cycling.
One reason for the desirability of printed circuit boards of the permanent resist design is that they will present a relative smooth surface if the pattern of conductive material and the pattern of photoresist material have substantially the same cross-sectional height. However, in the past there has not been available a photoresist material capable of being coated onto a substrate to a cross-sectional height of at least about 0.0015 inch and of maintaining that height without delamination during processing and use.
It has also been a problem that permanent resist materials which were previously available tended to delaminate from substrates after temperature cycling. There has been a need in the printed circuit board industry for a permanent resist material which will not delaminate after temperature cycling.
The delamination problems have also tended to frustrate commercialization of packages containing permanent resist printed circuit boards. There is a need for a permanent resist material which will enable the manufacture of packages containing two or more permanent resist printed circuit boards which will not delaminate in response to temperature cycling.